1. Field of the Invention
The present invention is directed to a light sensitive printing plate.
2. Description of the Prior Art
In the case that a light sensitive printing plate is exposed to light through an original, it has been hithertofore necessary that an additional resin layer be further provided on the surface of a light sensitive layer of the light sensitive printing plate, and the surface of the resin layer be intimately contacted with the original. For this purpose, there was employed a method which comprised placing a light sensitive printing plate and an original in laminated form between a rubber sheet and a glass sheet and pulling a vacuum between the rubber sheet and the glass to bring the system into intimate contact (hereafter simply referred to as a vacuum contact method). In conventional light sensitive printing plates, the surface thereof was smooth and close contact started at peripheral portions in the case that an original was intimately contacted therewith by means of a vacuum contact method. As a result, intimate contact at central portions was prevented. Therefore, in order to completely intimately contact an original over the whole surface of the light sensitive printing plate, an extremely long period of time was required. If image-wise exposure was conducted in a state of incomplete contact, a clear image could not be obtained at areas where close contact was incomplete so that a clear print was not obtained. In addition, if a long period of time was required for the intimate contact, the efficiency of printing was lowered. Accordingly, it has long been desired to shorten the contact time.
The inventors previously proposed providing on the surface of a light sensitive printing plate a matted layer capable of being removed upon development (Japanese Patent Application Nos. 31153/74 and 84902/74). When these light sensitive printing plates were employed under standard conditions, the vacuum contact time was remarkably shortened to one-half to one-third. However, it has been found that when these light sensitive printing plates were exposed to light in a large amount of 5 to 20 times the standard exposure amount, and subsequently developed under standard conditions, unclear portions were caused in dot image areas of the light sensitive printing plate.